1. Field of the Invention
This invention relates to liquid level gauges, and more particularly to gauges of the electronic type which utilize no moving parts.
More particularly, the invention relates to improvements in the gauge disclosed in U.S. Pat. No. 4,840,137 dated Jun. 20, 1989, entitled LIQUID LEVEL GAUGING APPARATUS, and having common ownership with the present application.
The entire disclosure of U.S. Pat. No. 4,840,137 is incorporated into the present application, by specific reference, in accordance with the practice set forth in MPEP .sctn..sctn. 608.01 (p), Revision 2, July, 1996.
2. Description of the Related Art Including Information Disclosed Under 37 CFR .sctn..sctn.1.97-1.99
U.S. Pat. No. 4,840,137 above identified illustrates and describes a liquid level gauge having a semi-transparent cup-shaped housing with a closed end, the end having a configuration which forms a light-refracting prism. Mounted inside the housing are a light source and a light sensor. In the disclosed embodiment, both the source and the sensor are secured in operative positions by a carrier block (72). The latter has seats for the source and sensor, such that they are positioned so as to be slightly convergent with respect to one another. Essentially, the gauge detects variations in the light that is reflected interiorly of the lens when the latter becomes immersed in liquid. Changes in the light arriving at the sensor are converted to measurements of liquid level in the area exterior of the lens.
Relatively high-resolution measurements are possible with the disclosed arrangement. Due to space requirements and auto-motive vehicle manufacturers' constraints, following the filing of the patent application which matured into this patent, the disclosed design was modified to incorporate an elongate internal printed circuit board that contained the various electrical circuitry which was necessary in order to power the light source, as well as processing the output from the light sensor.
As a consequence of such modifications, one proposal was the mounting of the light source and light sensor on a miniature p. c. board that itself was disposed perpendicular to the main p. c. board.
However, a distinct drawback resided in the assembly of the miniature p. c. board, and establishment of electrical connections between the miniature board and the main, elongate p. c. board.
Furthermore, where the gauge was subjected to vibration, as in automotive applications, it had to be capable of reliable operation and over extended periods of use.
A fairly concise explanation of the theory of operation of gauges of the type to which this invention relates is given in U.S. Pat. No. 4,998,022 issued Mar. 5, 1991, entitled OPTICAL LIQUID LEVEL SENSOR USING A POLYTETRAFLUOROETHYLENE PERFLUOROALKOXY MATERIAL, assigned to Conax Buffalo Corporation, Buffalo, N.Y. Specific reference is made to the first sheet of drawings of this patent, and the description beginning at line 10 of col. 6 thereof. The entire disclosure of U.S. Pat. No. 4,998,022 is also incorporated into the present application, by specific reference, in accordance with the practice currently set forth in MPEP .sctn..sctn. 608.01 (p).